Server caching can speed dynamic pages to near-static speeds. Many pages created by database queries only change every 15 minutes or so, e.g. CNN or Slashdot. Resin can cache the results and serve them like static pages. Resin's caching will work for any servlet, including JSP and XTP pages. It depends only on the headers the servlet returns in the response.
By default, pages are not cached. To cache, a page must set a HTTP caching header.
Resin's caching operates like a proxy cache. It's controlled by the same HTTP headers as any proxy cache. Every user shares the same cached page.
Setting theheader will cache the results until the time expires. For heavily loaded pages, even setting short expires times can significantly improve performance. Sessions should be disabled for caching.
The following example sets expiration for 15 seconds. So the counter should update slowly.
is useful for database generated pages which are continuously, but slowly updated. To cache based on something with a known modified date, like a file, you can use .
Theheaders let you cache based on an underlying change date. For example, the page may only change when an underlying source page changes. Resin lets you easily use by overriding methods in HttpServlet or in a JSP page.
The following page only changes when the underlying 'test.xml' page changes.
pages are useful in combination with the configuration.
Caching servlets is exactly like caching JSP pages (or XTP or static files.) Resin's caching mechanism works like a proxy cache: it don't care how the page is generated; as long as the proper caching headers are set, the page will be cached.
Resin can cache subpages even when the top page can't be cached. Sites allowing user personalization will often design pages withsubpages. Some subpages are user-specific and can't be cached. Others are common to everybody and can be cached.
Resin treats subpages as independent requests, so they can be cached independent of the top-level page. Try the following, use the firstcounter example as the included page. Create a top-level page that looks like:
In many cases, logged in users get specialized pages, but anonymous users all see the same page. In this case, you can still take advantage of Resin's caching, but you'll need to do a little work in your design.
First, you'll need to create ansubpage that contains the common page. The top page can't be cached because it depends on whether a user is logged in or not.
You must usebecause is cached just like the top page. The top page isn't cacheable because of the user login, so the forwarded page isn't cacheable either.
Here's what a sample subpage might look like:
The top page slightly trickier because it needs to pass the user to the subpage. You need to pass a unique id. If you pass a booleanparameter, all logged in users will see the same page.
Of course, the top-level page could also be a servlet:
Resin includes an anonymous user caching feature. If a user is not logged in, she will get a cached page. If she's logged in, she'll get her own page. This feature will not work if anonymous users are assigned cookies for tracking purposes.
To make anonymous caching work, you must set theheader. If you omit the x-anonymous header, Resin will use the to cache the same page for every user.
The top page must still set theor header, but Resin will take care of deciding if the page is cacheable or not. If the request has any cookies, Resin will not cache it or use the cached page. If it has no cookies, Resin will use the cached page.
When using x-anonymous, user tracking cookies will make the page uncacheable even if the page is the same for all users. Resin chooses to cache or not based on the existence of any cookies in the request, whether they're used or not.
assigns a browser Expires to an If-Modified cacheable page. It does not affect Expires cached pages and it does not affect Resin's caching. The FileServlet takes advantage of because it's an If-Modified servlet.
Often, you want a long Expires time for a page to a browser. For example, any gif will not change for 24 hours. That keeps browsers from asking for the same gif every five seconds; that's especially important for tiny formatting gifs. However, as soon as that page or gif changes, you want the change immediately available to any new browser or to a browser using reload.
Here's how you would set the Expires to 24 hours for a gif, based on the default FileServlet.
Theautomatically generates the Expires header. It only works for cacheable pages setting If-Modified or ETag. It will not affect pages explicily setting Expires or non-cacheable pages. So it's safe to create a cache-mapping for even if only some are cacheable.